Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, is a progressive neurodegenerative disease that affects nerve cells in the brain and spinal cord. ALS causes loss of muscle control, eventually leading to paralysis and death usually within 2 to 5 years from diagnosis. There is currently no cure for ALS, so early diagnosis is critical for managing symptoms and slowing progression. Many people wonder if a simple blood test could diagnose ALS, but unfortunately it is not that straightforward.
Are there blood tests for ALS?
While there is no single definitive blood test for ALS, certain blood tests may support an ALS diagnosis or rule out other potential causes. Some blood tests that may be relevant include:
- Complete blood count (CBC) – Rules out infection or inflammation.
- Electrolytes – Checks for imbalances like low potassium that can cause muscle cramps.
- Liver and kidney function tests – Helps rule out toxicity or disease.
- Thyroid tests – Rules out thyroid disorders causing muscle weakness.
- Glucose tests – Rules out diabetes contributing to nerve damage.
- Creatine kinase – Measures muscle breakdown which is elevated with ALS.
- Erythrocyte sedimentation rate (ESR) – Marks inflammation associated with motor neuron damage.
- Immunoglobulin tests – Detects abnormal antibodies targeting nerve cells.
- Heavy metals screen – Rules out toxic exposures like lead or mercury.
While these tests may provide clues, none can definitively diagnose or rule out ALS. Abnormal results typically prompt further testing. Normal bloodwork does not mean a person will not develop ALS later on. The disease causes gradual damage to nerve cells over time before symptoms appear.
Are there specific protein markers for ALS in blood?
Scientists are studying whether specific proteins released during motor neuron breakdown could serve as ALS biomarkers detectable in blood. Some promising markers include:
- Neurofilaments – Structural proteins inside nerve fibers that rise as neurons degenerate.
- TAR DNA-binding protein – Involved in DNA repair and elevated with neuronal stress.
- C-reactive protein – A marker of inflammation and immune activation in ALS.
- Cystatin C – Associated with breakdown of the blood-brain barrier in ALS.
Levels of these proteins may correlate with ALS progression and response to treatment. However, more research is needed before they can be used clinically. Currently there is no blood test utilizing a single or pattern of protein biomarkers that can definitively diagnose ALS in an untreated individual.
Can genetic testing diagnose ALS?
There are over 25 genes associated with familial ALS, an inherited form of the disease. Genetic testing can detect mutations known to directly cause ALS, like in the C9orf72, SOD1, TARDBP, and FUS genes. However, familial ALS accounts for only 10% of cases. The majority are sporadic with no family history. Furthermore, some genetic variants merely increase susceptibility but do not directly trigger motor neuron degeneration on their own. Therefore, genetic testing alone cannot definitively diagnose sporadic ALS but it can provide supportive information in the right clinical context.
Uses of genetic testing in ALS:
- Diagnose familial ALS if a known causative mutation is found.
- Assess inherited risk in relatives of familial ALS patients.
- Guide prognosis based on genotype-phenotype correlation.
- Select clinical trial eligibility for targeted gene therapies.
- Provide insight on disease mechanism and customized treatment.
While useful in many ways, a negative genetic test does not rule out sporadic ALS. The complex interplay between environment, lifestyle, and multitudes of gene variants beyond current knowledge likely contribute to disease risk.
What tests confirm an ALS diagnosis?
There is no single confirmatory test for ALS. Instead, diagnosis relies on assessing characteristic signs and symptoms and ruling out mimicking disorders. Key tests used to support a clinical ALS diagnosis include:
Electromyography (EMG)
An EMG tests the electrical activity of muscles and peripheral nerves. It can detect abnormalities and nerve dysfunction consistent with ALS. However, EMG is not fully conclusive on its own.
Nerve Conduction Studies
These studies measure how quickly electrical signals travel through a peripheral nerve. Slow nerve conduction velocities indicate nerve damage seen in ALS.
MRI of the Brain and Spinal Cord
MRI scans can visualize detailed structures and check for issues like nerve inflammation, compression, tumors, or disorders mimicking ALS. About 10% of suspected ALS cases have an alternate MRI diagnosis.
Muscle Biopsy
Removing a small muscle sample to examine nerve-muscle connections microscopically can support a diagnosis of ALS. However, it cannot confirm or exclude ALS with certainty.
In addition to these tests, assessing symptom progression over time remains key. Only the clinical context and gradual development of upper and lower motor neuron signs and symptoms can lead to an accurate ALS diagnosis. Blood tests provide supporting data at best.
What blood tests help monitor ALS progression?
Periodic blood tests during ALS management can help evaluate disease progression and track health impacts. Some examples include:
| Blood Test | Purpose in ALS Monitoring |
|---|---|
| CBC | Checks for infection during immunity decline in ALS. |
| Liver enzymes | Monitor liver health with nutrition issues and medication side effects. |
| Kidney function | Assess kidney function if mobility and hydration are impaired. |
| Glucose | Monitor increased diabetes risk with steroid treatments. |
| Cholesterol | Manage cholesterol and vascular health with reduced mobility. |
| Creatine kinase | Trend muscle breakdown as ALS advances. |
| Thyroid hormone | Evaluate thyroid levels that may be impacted by ALS. |
Tracking these measures over time allows your ALS healthcare team to assess disease progression and modify treatments accordingly to slow decline and maximize quality of life.
Conclusion
In summary, there are currently no blood tests that can definitively diagnose ALS. However, certain bloodwork can support the diagnostic process by highlighting indicators of disease, uncovering alternative explanations for symptoms, and monitoring impacts over time. While promising research on biomarkers and genetics continues, expert clinical evaluation based on symptom progression remains the gold standard for ALS diagnosis. Blood tests serve as just one piece of the complex puzzle. Increased awareness of ALS and early consultation with a neurologist specializing in motor neuron disease is key for accurate identification and timely intervention.